The present invention relates to a protocol translation method and protocol translation apparatus, and more particularly to a protocol translation method and apparatus suitable for intercommunications between an IPv4 terminal existing in an IPv4 network and a Mobile IPv6 terminal existing in an IPv6 network.
In recent years, a serious problem has arisen due to widespread use of Internet Protocol (IP). That is, the number of IP addresses available is insufficient. It is anticipated that this IP address depletion problem will be exacerbated with accelerating speed because an increasing number of devices other than personal computers (PCs) will be connected to Internet. Under these circumstances, there is an increased necessity for switching to the next-generation IP standard named “IPv6 (Internet Protocol version 6)”, which has a vast address space (128-bit long addresses) and offers improved security functions, priority control functions, automatic configuration functions, and various other enhanced functions.
When formulating a detailed plan for switching from IPv4, which is the current IP standard, to IPv6, however, it is necessary to replace routers and other devices and replace and/or add software for the purpose of making an existing IPv4 network compliant with IPv6. Such a changeover would entail enormous cost. Further, there is a risk of affecting operations when you replace running devices or add new functions. As such being the case, it is necessary to make a gradual transition to IPv6 without seriously affecting currently used IPv4 networks. It must be pointed in this connection that the technology for providing intercommunications between these two different networks is required over a transitional period during which IPv4 and IPv6 networks coexist.
To establish communication between devices having IPv4 communication functions only and devices having IPv6 communication functions only, it is necessary to provide translation between IPv4 packets and IPv6 packets at a certain point in an intermediate route. This translation is performed by an IPv4/IPv6 translation apparatus.
An IPv6 terminal has a 128-bit IPv6 address, whereas an IPv4 terminal has a 32-bit IPv4 address. These addresses are used for terminal identification. However, these two terminals differ in the addressing system and cannot identify the address of the other terminal. When IPv6 terminals and IPv4 terminals communicate with each other as shown in FIG. 1, therefore, the IPv4/IPv6 translation apparatus must assign tentative virtual IPv4 addresses to the IPv6 terminals and tentative virtual IPv6 addresses to the IPv4 terminals. When assigning the virtual addresses, the IPv4/IPv6 translation apparatus uses addresses it retains. Further, IPv4 addresses can be embedded in the 32 low-order bit positions of an IPv6 address. Therefore, an IPv6 address having an embedded IPv4 address can be used as a tentative virtual IPv6 address of an IPv4 terminal. The example shown in FIG. 1 indicates that a tentative virtual IPv4 address (192.168.0.1) is assigned to IPv6 terminal A by an address management table 60.
One publicly known example is the Internet Engineering Task Force's (IETF's) “Network Address Translation—Protocol Translation (NAT-PT)” (RFC (Request For Comment) 2766).
Meanwhile, PCs having mobile communication functions are now capable of connecting to a nearby network after a move to receive services in a so-called mobile computing environment. At present, Mobile IPv6 and other protocols are proposed as a standard procedure to be performed by nodes (PCs, PDAs, and other computer network terminals) for establishing communication.
In Mobile IPv6, each terminal has two IP addresses as shown in FIG. 2: home address and care-of address. The care-of address varies with the connected subnetwork when the terminal moves. The home address, on the other hand, remains unchanged not matter whether the terminal moves. A home agent uses its incorporated storage section to memorize an address management table, which defines the relationship between the home address and care-of address. The home agent receives a packet containing a new care-of address from a moved Mobile IPv6 terminal and updates the associated address management table data.
When there is an intention to establish communication with a Mobile IPv6 compliant terminal (hereinafter referred to as a Mobile IPv6 terminal) but its care-of address is not known, a packet is transmitted to the home address of that Mobile IPv6 terminal. In Mobile IPv6, the home agent receives the packet that is transmitted to the home address, and transfers the received packet to the care-of address of a Mobile IPv6 terminal that corresponds to the home address. Mobile IPv6 communication is established in this manner.
The technology concerning the above-mentioned Mobile IPv6 terminal communication is described in JP-A No. 268129/2001.